The present invention relates to a printing apparatus with a printing roller provided with a profile which comprises raised and lowered parts in circumferential direction, a printing belt provided at one side with a complementary profile, and an opposite roller which together with the printing roller determines a nip through which the printing belt runs, in such a way that its profile side interacts with the printing roller, and its printing side interacts with the opposite roller.
Such a printing apparatus is known from Dutch Application 8700431. In the case of this known printing apparatus the printing belt is made of a flexible, rubber-like material on which printing plates containing the printing image are placed. The flexible belt is provided with teeth running in the crosswise direction which interact with complementary teeth provided on the printing roller. The purpose of these interacting teeth is to position the printing plates correctly with the web of paper to be printed, which must also be guided through the nip between printing roller and impression roller.
This known printing apparatus has various disadvantages. The first disadvantage is that the flexible printing belt has a varying flexural rigidity, viewed in its lengthwise direction. At the position of the teeth the printing belt is thicker and therefore more rigid than at the places between the teeth. This means that the printing plates do not run in an accurate circular shape around the printing roller and through the nip, but at the position of the teeth are more flattened than at the places between the teeth. This leads to imperfections in the image printed on the web of paper.
A further disadvantage of this known printing belt arises from the fact that it is made of relatively flexible material. As a result of the undercut, in other words the distance over which the impression roller presses in the printing belt, a certain displacement of the flexible material occurs at the position where it is pressed in. This displacement manifests itself in a widening of the pressed-in material, which leads to the image on the printing plates also being widened. A point in the image to be printed, for example, acquires greater dimensions as a result, which adversely affects the printing obtained on the paper web.